John, I don't think that anybody's actually suggesting that we add
server discovery in here. :) But since the server does echo back the
configuration in its response, the client is discovering a few things at
run time about what it can and can't do with a particular server. It's
entirely possible that the client might get back a configuration option
that it can't use (say, it can't do client_secret_jwt assertions but it
can do
From what I can see from this thread though there are two open
questions that Phil's raised:
1: Extensibility of token_endpoint_auth_method values, and where
potential values are listed (IANA? fully qualified URIs for things not
in the base spec?)
2: Plurality of token_endpoint_auth_method (could be left as a string,
made an array, or be a JSON-style optional plural: string value if
singular or array if plural)
I think the first one should be addressed, but we just need to pick the
method. I'm personally in favor of the same method we used for
grant_type, which is short values in the spec and extensions as fully
qualified URIs. The second one could break existing implementations (and
other dependent specs), so if we change it, it has to be for very good
reason.
-- Justin
On 04/24/2013 07:23 PM, John Bradley wrote:
In Connect there is a AS discovery before registration.
The general pattern is the RP discovers the capabilities of the AS
authentication methods and algorithms supported by the AS.
The client then picks the best options for it and registers them.
It would in theory work of the client knowing nothing about the AS
pushed it's capabilities at the AS as you are suggesting and let the
AS pick.
My general feeling is that discovery with the client picking the
options works best.
In many cases the client doesn't need to register parameters as they
can be selected at run time once it knows what a server supports.
The token endpoint authentication method was a bit of a special case
where even though it could be all dynamic and work, you do want to
register a choice to prevent backwards compatibility attacks.
I don't really want to complicate registration by trying to make it
also cover AS discovery.
John B.
On 2013-04-24, at 7:55 PM, Phil Hunt <[email protected]
<mailto:[email protected]>> wrote:
Right and if the client wants a method not supported then what?
Why can't the client offer up a list of methods it is able to
support, say in order of preference?
The text appears to indicate only one value may be passed.
Given the way it is written. It seems better to just have the server
say the client must do authn method X in the response.
Phil
@independentid
www.independentid.com <http://www.independentid.com/>
[email protected] <mailto:[email protected]>
On 2013-04-24, at 3:41 PM, John Bradley wrote:
In Connect the AS may support a number of token endpoint
authentication methods. The reason to allow a client to register
using a particular one is to prevent downgrade attacks.
If the client wants to always use an asymmetric signature you don't
want to allow attackers to use weaker methods like http basic.
So a server may support any number of methods, but it is reasonable
for a client to specify which one it is going to use. In a closed
system that may not be that useful but in a open system where the AS
has a looser relationship to the client it is important.
John B.
On 2013-04-24, at 7:30 PM, Phil Hunt <[email protected]
<mailto:[email protected]>> wrote:
Hmmm… what was the objective or use case for having the client
being able to choose in the first place?
It seems to me that the AS will make a decision based on many
factors. As you say, there isn't any other place that enumerates
the various [authn] methods a client can use to access the token
endpoint. So, why do it?
Phil
@independentid
www.independentid.com <http://www.independentid.com/>
[email protected] <mailto:[email protected]>
On 2013-04-24, at 2:07 PM, Justin Richer wrote:
Seems reasonable to me, can you suggest language to add in the
capability? Would it require an IANA registry? Right now there
isn't any other place that enumerates the various methods that a
client can use to access the token endpoint.
-- Justin
On 04/24/2013 04:17 PM, Phil Hunt wrote:
For parameters to token_endpoint_auth_method, the spec has
defined "client_secret_jwt" and "private_key_jwt". Shouldn't
there be similar options of SAML?
Shouldn't there be an extension point for other methods?
Phil
@independentid
www.independentid.com <http://www.independentid.com/>
[email protected] <mailto:[email protected]>
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